The present invention is generally concerned with improvements in or relating to dental cements, among others, glass ionomer cements. In particular, it pertains to a novel liquid for setting dental cements which excels markedly in crushing strength, water resisting property and manipulation characteristics during mixing.
The glass ionomer cements that have main use in dentistry are prepared by setting fluoroaluminosilicate glass and a polycarboxyic acid such as polyacrylic acid under the presence of water, and their appearance is good thanks to the transparency of the glass mixed-in. In particular, the cements of this type have little or no detrimental corrosive or other harmful pathological action upon the pulp, exhibit satisfactory adhesion to both teeth, dentin and enamel, excel in marginal sealing property and maintain their resistance to the mouth tissues or fluids over an extended period of time. Owing to their unique capabilities, from which is free the commerically available composite resin of the resin type, the glass ionomer cements find important use as restorations, for anterior teeth and as binders for prostheses, other linings or building-up. However, the glass ionomer cements which comprises a mere combination of an aqueous solution of polyacrylic acid and powders of fluoroaluminosilicate glass have now been found to be disadvantageous in that they provided a mixed product which is inferior in fluidity and manipulation characteristics, and takes a longer period of time for setting. As a result, the mixed product comes at its surface into contact with the oral fluids and disintegrates to such an extent that it becomes brittle, thus resulting in a lowering of the final strength. Laid-open Japanese Patent Application No. 101893/1977 specification discloses a process that does not offer such problems, and yet has advantages over the prior art. According to this process, 7 to 25% by weight of one or two or more of polybasic carboxylic acids are added to a 45 to 60% by weight aqueous solution of polyacrylic acid to prepare a setting liquid. In fact, this liquid is easy manipulate so that setting is complete within a short period of time, and gives rise to increases in strength. When used as fillings for oral restorations, however, the setting liquid as referred to above is susceptible to the mouth fluids and humidity, and has a cloudy tendency. For this reason, it is ordinarily required to apply a waterproofing treatment which comprises coating a waterproof varnish on the surface of the mixed product followed by sufficient drying, to thereby form a waterproof film. These procedures are tolerably troublesome and time-consuming as compared with the manipulation for filling the composite resin for the dental restoration.